Packaging machine

ABSTRACT

A packaging machine including a supply of film for wrapping a package and a hot plate for heat fusing the film of a wrapped package. Power to the heating element is only delivered to the element during a heating cycle, thus conserving electrical power. A photo eye senses the package and a control circuit energizes the heating element the element reaches a desired heating temperature in 2 to 4 seconds. The frame of the machine includes a lower base member to which an upper base plate, preferably formed from a continuous sheet, is rigidly attached. The upper plate includes a support surface for the hot plate, a vertical wall to which the photo eye is attached that is interconnected with the support surface by a curved transition surface. The upper base plate also includes a lateral, rearwardly extending plate portion which defines at least a portion of a hardware enclosure.

RELATED APPLICATION

This application is a continuation-in-part of U.S. patent application Ser. No. 13/382,347, filed Jan. 5, 2012, which claims the benefit of International Patent Application PCT/US2010/041368, filed Jul. 8, 2010, which claims the benefit of 61/223,761, filed Jul. 8, 2009, the disclosure of which is entirely incorporated herein by reference.

TECHNICAL FIELD

The present invention relates generally to packaging systems, and, in particular, to a new and improved package wrapping machine.

BACKGROUND ART

Packaging machines of the type that are used to hand-wrap packages with a thin, often clear film, are often used in supermarkets to wrap meat, cheese, etc. In a typical machine, a foam tray on which the meat or cheese is placed is hand-wrapped with a length of stretchable film that is dispensed from a roll on the wrapping machine. Once wrapped, the film is severed and the edges of the sheet are folded and tucked on the underside of the package. Heat is then used to fuse the film, thus sealing the package. In a typical machine, a hot plate surface is provided which is heated to a predetermined temperature that is related to the temperature needed to cause melting or fusion of the film used to wrap the package.

DISCLOSURE OF INVENTION

The present invention provides a new and improved packaging machine of the type that is used to hand-wrap a package with a stretchable film. The present invention provides a supply of film for wrapping a package, a means for severing a length of the film and a hot plate surface for effecting fusion and sealing of the film that is wrapped around the package.

In accordance with a feature of the invention, the presence of a package to be sealed is sensed when a package is placed on a hot plate mechanism and/or when the hot plate mechanism is depressed by the operator. The sensing of a package triggers a control circuit which energizes a heating element forming part of the hot plate mechanism and which is arranged to reach a predetermined operating temperature in less than ten seconds, preferably in 2 to 4 seconds.

According to another feature of the invention, the heating element is only energized for a predetermined interval of time whenever a package to be sealed is set on it. As a result, substantial electrical power is conserved since the heating element is only energized when a package to be sealed is present and only for a predetermined length of time.

In the preferred and illustrated embodiment, a hot plate subassembly is provided that includes a heated platform that is pivotally attached to a base by a lever arm. In the illustrated embodiment, a biasing spring urges the heated platform to a raised position. A position sensor, i.e., a micro-switch, changes state when the platform moves from its raised position to a package sealing position.

The change in state detected by the micro-switch activates a timer circuit that energizes a heating element forming part of the hot plate platform in order to provide heat for sealing/fusing the packaging film.

According to a preferred embodiment, the length of time during which the heating element is energized, is determined by an interval timer having a predetermined time-out interval and which is also connected to a temperature sensor. In the illustrated embodiment, a time-out interval is controlled by an external resistor (which may be selectable by the operator), and the thermistor that monitors the temperature of the heating element.

When a package to be sealed is placed on the platform, downward movement of the platform causes the micro-switch to change state and apply power to the hot plate interval timer. If the heating element does not exceed a predetermined temperature during the sealing cycle, the heating element will be energized for the full cycle time determined by the selected resistance. However, if the desired temperature is reached prior to the end of the sealing cycle, the thermistor (which monitors the temperature of the heating element) will cause the timer to immediately time-out and interrupt power to the heating element.

According to another feature of the invention, a separate interval timer is used to activate a light indicator (or other signaling device, such as a buzzer) in order to provide a visual means to an operator that the machine is in a heat sealing cycle. With this arrangement, the indicator light remains illuminated for the full sealing time, even though power to the heating element may have been interrupted because it reached its maximum operating temperature. With this arrangement, the package being sealed will not be inadvertently removed from the platform prior to full sealing of the packaging film.

According to a further feature of the invention, the hot plate subassembly is pivotally attached to a sub base which, in turn, is fixed to a machine base. An axle rotatably supported by flange bushings in the lever arm are secured to upturned flanges formed in the sub base.

According to another feature of the invention, the sealing times are selectable by the operator and in the illustrated embodiment are provided by a multi-positioned switch which connects selected resistors to appropriate terminals on the interval timers. The selected resistors determine the amount of time a given timer will connect power to its associated device.

According to another embodiment of the invention, a packaging machine of the type for wrapping packages with a stretchable film is disclosed that has a frame, a supply of wrapping film, a film severing device and a hot plate having a heating element for fusing at least a portion of the film that is wrapped around a package. The alternate embodiment of the machine includes a non-contact or proximity sensor forming part of a heating circuit for the heating element that applies power to the heating element when a package is sensed. In the preferred and illustrated alternate embodiment, the sensor comprises a photo eye assembly that is arranged such that it senses the package to be sealed as it is placed on the hot plate. According to a preferred feature of this embodiment, the heating element is energized for as long as a package to be sealed is sensed by the photo eye assembly.

According to another feature of this embodiment, a temperature responsive device associated with the heating element is operative to deenergize the heating element if a predetermined operating temperature is exceeded. The alternate embodiment preferably includes a temperature controller which is capable of modulating power to the heating element to maintain the heating element at a predetermined temperature rather than fully deenergizing the heating element when a preselected temperature is reached, as is the case with the first embodiment. According to a further feature of the preferred embodiment, a feedback component such as a thermistor or thermocouple is used to sense temperature of the heating element and this temperature information is communicated to the temperature controller which, in turn, may modulate power to the heating element in accordance with the temperature information received from the feedback component. In the illustrated alternate embodiment, an interval timer is also used in order to control the maximum time that the heating element can be energized when a heating cycle is initiated upon sensing of a package to be sealed on the hot plate.

In accordance with the alternative embodiment, a packaging machine frame is provided which includes a lower base member having integrally formed side plates and laterally extending tabs that define a mounting location for a cut-off rod. The lower base member also includes at least one upturned mounting flange.

The frame also includes an upper base plate that defines a substantially horizontal support surface for the hot plate and a vertical wall that is interconnected with the support surface by a curved transition portion. The upper base plate further includes a substantially laterally extending enclosure portion for defining a portion of a hardware enclosure located between the side plates of the lower base member when the upper base plate is mounted to the lower base member. The upper base plate further includes at least one downwardly depending flange that is engageable with the upturned flange defined by the lower base member.

The disclosed frame construction allows for easy maintenance and cleaning of the packaging machine and the construction is adaptable to a wide variety of packaging machines of the type to which the invention pertains and may be incorporated, for example, in the packaging machine of the first embodiment.

According to a feature of the alternate embodiment, the photo eye assembly is mounted and carried by the vertical wall portion of the upper base plate. According to another feature of this embodiment, a vertical plate member is used to join the enclosure portion of the upper base plate with the lower base member.

Additional features of the invention will become apparent and a fuller understanding obtained by reading the following detailed description made in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is an isometric view of a wrapping machine constructed in accordance with a preferred embodiment of the invention;

FIG. 1B is an exploded view of the machine shown in FIG. 1A;

FIG. 2 is a sectional view through the center of the machine shown in FIG. 1A;

FIG. 3 is a perspective view of a hot plate mechanism constructed in accordance with the preferred embodiment of the invention;

FIG. 4 is an exploded view of the hot plate mechanism shown in FIG. 3;

FIG. 5 is a block diagram of the control system for a hot plate heater;

FIG. 6 is a schematic of a circuit that controls the heating of the hot plate shown in FIG. 3, as well as a rod for severing the packaging film from a supply roll;

FIG. 7A is a block diagram of an alternate control system for a hot plate heater;

FIG. 7B is a schematic of an alternate circuit for controlling the heating of the hot plate shown in FIG. 3;

FIG. 8 is an isometric view of a wrapping machine constructed in accordance with another preferred embodiment of the invention;

FIG. 9 is a sectional view through the center of the machine that is shown in FIG. 8 and is similar to the view shown in FIG. 1A;

FIG. 10A is a block diagram of an alternate control system for a hot plate heater shown in FIGS. 8 and 9; and

FIG. 10B is a schematic of the control system shown in block diagram form in FIG. 10A.

BEST MODE FOR CARRYING OUT THE INVENTION

FIGS. 1A, 1B illustrate a wrapping machine constructed in accordance with a preferred embodiment of the invention. As is known, this type of machine is used to wrap packages with a stretchable, heat-sensitive film. Once the package is wrapped, heat is used to fuse the wrapping in order to seal the package. This type of machine is often used in supermarkets to package produce, meats, etc.

The illustrated wrapping machine is considered a tabletop machine. It should be understood, however, that the principles of this invention, to be described, are equally applicable to floor and self-standing wrapping machines.

As seen best in FIG. 1B, the machine includes a frame indicated generally by the reference character 10 that comprises a pair of side plates 14, 16 and base 18. In the preferred embodiment, the frame is made from aluminum and is formed from a single sheet of material formed into the U-shape shown in FIG. 1B.

A roll of stretchable packaging film 20 is supported for rotation by a pair of supports indicated generally by the reference characters 21, 22 (see FIG. 1A). In the illustrated embodiment, each support comprises a pair of support blocks 24, 26 that are clamped together by a pair of threaded studs or screws 28 and associated wing fasteners 30. The roll 20 itself is mounted to a reusable roll support that comprises end pieces or flanges 34 and an axle 36. The ends of the axle 36 are removably captured between the support blocks 24, 26. When the supply of wrapping material is exhausted, the roll support is removed from the machine by removing the wing nuts 30 to enable the upper support block 24 to be removed. This releases the ends of the axle 36 and allows the operator to install a fresh supply of wrapping material or film.

A pivotally mounted plate or bridge 40 defines a wrapping surface 40 a upon which a package is wrapped with film from the supply 20. The bridge 40 includes a pair of downwardly depending end flanges 40 b which overlie the outer, upper edge surfaces of the side plates 14, 16 and a rigidizing back flange 40 c. Gaps 41 d provide clearance for the upper edge of the side plates 14, 16. This construction provides support for the bridge when rotated into its horizontal position shown in FIG. 1A. The bridge 40 can be pivoted upwardly about a pivot 42 to expose the inside of the machine including its electrical box 46. As seen best in FIG. 2, a cover plate 46 a encloses the electrical components housed within the box 46. The cover 46 a covers a compartment 48 which houses circuitry and other components necessary for the operation of the machine.

The wrapping material is dispensed from the roll 20 along the path P. The material is guided by the cover 46 a and emerges through an opening defined between the front edge 41 of the bridge 40 and a retainer rod 50. In the preferred and illustrated embodiment, the retainer rod 50 is covered with a coating, i.e., vinyl, to which the wrapping material releasably adheres so that the end of the material is maintained and positioned for easy grasping by the operator. The cover 40 is pivoted upwardly (as viewed in FIG. 2) to expose the feed path and facilitate feeding of the wrapping material.

The package to be wrapped is placed on the bridge 40 and a suitable length of film material is pulled from the supply by the operator. The operator then hand wraps the material around the package.

When the wrapping material fully encompasses the package, the portion of the wrapping surrounding the package is severed from the rest of the web by preferably contacting a heated rod 58. Since the material is heat sensitive, contact with the heated rod causes severance of the material.

In general, once the wrapped package is severed from the rest of the web, the wrapping is gathered, tucked or folded underneath the package. According to the invention, the side of the package with the gathered/folded material is placed upon a hot plate subassembly indicated generally by the reference character 60 which includes a heated hot plate 64. The heat from the hot plate 64 causes fusion of the material and, hence, seals the package.

According to the invention, the hot plate 64 is not energized or heated until a package is placed on its sealing surface 64 a. According to the preferred embodiment and, as best seen in FIGS. 2 and 3, the hot plate or heated platform 64 is pivotally attached to the base 18 by a lever arm assembly 66 which includes a lever arm 66 a and a sub-base 66 b. The lever arm 66 a is best shown in FIG. 4 and includes a pair of side plates 67 a, a rear plate 67 b, a top plate 67 c and a support plate 67 d to which the hot plate 64 is attached by a plurality of fasteners 69. The lever arm 66 a mounts an axle 68 which, as seen in FIG. 3, includes ends that extend beyond the side plates 67 a. The sub-base 66 b includes a plurality of mounting holes 65 by which the sub-base 66 b is rigidly attached to the base 18. The sub-base 66 b includes a pair of parallel, upturned flanges 71, which include apertures 71 a, by which fasteners 71 b are used to secure ends of the axle 68 to the flanges 71 and which thus pivotally support the lever arm 66 a. The axle 68 is preferably supported by flanged bushings 73.

In a preferred and illustrated embodiment, and as best seen in FIGS. 1A and 2, an indicator light 75 (i.e., LED) is mounted to the top plate 67 c of the lever arm 66 a. In the preferred embodiment, the LED is energized to indicate to an operator that the machine is in a heating/sealing cycle.

As seen in FIGS. 2 and 3, the hot plate subassembly 60 includes a micro-switch 70 that is secured to the back plate 67 b of the lever arm 66 a and which includes an actuating plunger 72. In the illustrated embodiment, when the hot plate subassembly 60 is in its upper position as viewed in FIG. 2, the plunger 72 is depressed by contact with the sub-base 66 b. When a package is placed on the hot plate surface 64 a, either the pressure of the operator or the weight of the package or both causes the hot plate to move downwardly as viewed in FIG. 2, thereby causing upward movement in the opposite end of the lever arm 66 a which, in turn, causes the micro-switch plunger 72 to be released allowing it to move outwardly (downwardly as viewed in FIG. 2). In the preferred embodiment, the hot plate subassembly is biased towards its upper position shown in FIG. 2 by a tension spring 76 that is captured by a lug 78 forming part of the lever arm 66 a and a lug 79 secured to the sub-base 66 b (shown best in FIGS. 3 and 4).

As is known, the plunger 72 is coupled to normally closed (N/C) and normally opened (N/O) contacts within the micro-switch 70 which open and close, depending on the position of the plunger 72. As will be explained, the micro-switch 70 is used to control the energization of the indicator light 75 and a heating element forming part of the hot pate 64. It should be noted here, that the location of the micro-switch can be varied and, may in fact, be positioned further upstream from the hot plate 64 should earlier energization of the hot plate be desired.

Referring to FIG. 4, the details of the hot plate construction are illustrated. In addition to what has already been described, the hot plate 64 includes a base plate 80 which may be fiberglass, a sheet of insulation 82 and a heating element 84, all of which are sandwiched together by a pair of longitudinal frame rails 86 and a pair transverse frame rails 88. In the preferred embodiment, a temperature monitoring thermistor 89 having connection wiring 89 a is attached (as by taping) to the insulation sheet 82. In the preferred embodiment, a heat sink pad 91 is provided to buffer the heat generated by the heating element 84. The heat sink pad 91 allows the use of a thinner heating element layer. In the preferred embodiment, the heat sink pad is graphite and this type of material is available from EGC Enterprises, Inc., of Chardon, Ohio. Fasteners, including a plurality of nuts and washers, are used to maintain the assemblage.

As seen best in FIG. 4, the base plate 80 is rigidly fixed to one side of the lever arm 66 by suitable fasteners. The base plate 80 and insulation sheet 82 include respective access holes 80 a, 82 a through which wiring W (shown in FIG. 3) for the heating element 84 are fed.

According to the invention, the heating element 84 is capable of reaching a desired operating temperature sufficient to provide sealing of the package in less than 10 seconds. This is achieved by utilizing a graphite-based heater and a suitable control circuit. According to the invention, the micro-switch 70 is used to sense the presence of a package on the hot plate 64 i.e. when a package is placed on the hot plate, the resulting downward movement of the lever arm 66 causes the micro-switch to change state. The micro-switch forms part of a power circuit for providing power to the heating element 84 sufficient for it to reach a desired operating temperature within a very short period of time, i.e., 2 to 10 seconds. In the preferred and illustrated embodiment, the heating element 84 is of a rapid, response flexible graphite foil heater, an example of which is available from EGC Enterprises, Inc., of Chardon, Ohio.

The ability for the hot plate to quickly reach the desired temperature is further achieved by reducing the thermal mass of the hot plate 64, thus reducing the thermal time constant for the apparatus. As noted above, the base plate 80 is preferably constructed of fiberglass which has a relatively low mass. In addition, the insulation sheet 82 is also of a low mass material. One such material is sold under the “AEROGELS” brand and is sold by Aspen Aerogels, Inc. of Northborough, Mass. In addition, the heating element 84 is selected to have a low mass as well. In the preferred construction, the relatively low mass of the overall hot plate 64, coupled with the rapid response time of the preferred heating element 84, provides a hot plate with a very rapid response time. In the preferred embodiment, the heater reaches the desired operating temperature from ambient in 2 to 4 seconds.

FIG. 5 illustrates a block diagram of the control system for energizing the hot plate 64. The block 100 represents a source of power, in this case, AC power. AC power is fed to the micro-switch or cycle start switch 70 (the details of which will be described later) and to a pair of interval timers 106 a, 106 b. In the preferred and illustrated embodiment, the interval timer 106 a is a relatively low powered timer, (i.e., 1 amp) and is used to control the energization of the light indicator 75 and/or a signaling buzzer 75 a. The interval timer 106 b has the capability of controlling significant power, (i.e., 30 amps) and is used to control the energization of the heating element 84.

As seen in FIG. 5, both timers 106 a, 106 b are initiated by a change of state in the cycle start switch 70 (which is mounted to the lever arm 66 a). The length of time that the timers 106 a, 106 b apply power to their respective devices is determined by external resistors. In the preferred embodiment, a multi-position, rotary or slide switch 114 is used to connect suitable resistances to the timers 106 a, 106 b. The resistance selected determines, in part, how long a given timer will apply power to its associated device. In the preferred embodiment, the timer 106 a energizes the light indicator 75 (and/or the buzzer 75 a) for a length of time totally determined by the resistance selected. The interval timer 106 b, however, applies power to the hot plate heater 84 as a function of both the resistor selected and the thermistor 89 that monitors the temperature of the heating element. In particular, the resistance selected and connected to the interval timer 106 b determines the maximum time that power will be applied to the heating element. However, if the thermistor senses that the desired temperature is reached prior to the time determined by the resistor, the timer 106 b will time-out and interrupt power to the heater 84. During periods of heavy usage, the actual time that power is applied to the hot plate heater 84 is substantially shorter than the heating cycle time determined by a given resistor. It should be noted, that because the indicator light 75 is controlled by an independent timer, the sealing time, as observed by the operator by virtue of the indicator light, remains unchanged, even though power to the hot plate heater may be terminated. As a result, consistent sealing of packages is assured, as compared to a circuit in which an indicator light is only illuminated when power to the hot plate 84 is applied.

FIG. 6 is a schematic for a control circuit for the hot plate heater. In the illustrated embodiment, the circuit is powered from a 115 volt AC receptacle. The circuit includes a power switch 200 which, when closed, provides power to the heated rod cutter element 58 (shown in FIG. 1A), and the micro-switch 70 (also termed cycle start switch). As seen in FIG. 6, the temperature of the cutter element 58 is controlled by a conventional circuit carried on a circuit board 58 a, which is supplied by TUTCO Inc. of Cookeville, Tenn. The switched leg of the AC power is connected to the cycle switch 70, the hot rod cutter circuit 58 a, and one side of a heat indicating light 75. The micro-switch 70 forming part of the hot plate platform and seen best in FIG. 3 is represented in the schematic by the double pole switch 70 termed a cycle start switch in FIG. 6. It is shown with the normally open (N/O) contacts closed because when the platform is in the upper position, the plunger 72 is depressed which opens the normally closed (N/C) contacts and closes the normally open contacts. When the platform is moved downwardly by placement of the package on the heating surface 64 a, the state of the switch 70 changes so that the normally open contacts open and the normally closed contacts close. The closure of the normally closed contacts causes power to be fed to pins 21 (+pins) of the interval timers 106 a, 106 b. This change in switch position causes activation of the timers 106 a, 106 b and causes these timers to apply power to their associated devices, depending on the external resistance connected to a given timer. In the case of the interval timer 106 a (which controls the activation of the indicator light 75), a selected external resistance is applied to its terminals 34, 33, the value of the resistance being determined by the position of the switch 114.

In the case of the interval timer 106 b (which provides power to the heating element 84), its time-out is determined by the external resistance applied to its associated terminals 25, 24. As seen best in FIG. 6, the actual resistance applied to these terminals is determined by the position of the switch 114, as well as the thermistor 89. The time-out of the interval timer 106 b can vary for a given position of the switch 114. The timer interval is also determined by the temperature of the heating element 84 as measured by the thermistor 89. As a result, and especially during heavy usage, the interval of time during which power is applied to the heating element 84 may be substantially shorter than the actual sealing cycle time as indicated by the interval timer 106 a.

With the preferred construction, when a package is placed on the hot plate 64, the resulting downward movement of the hot plate causes the micro-switch 70 to deactivate which, in turn, causes the energization of the timers 106 a, 106 b for a predetermined time determined by the external resistance selected by the switch 114 and the thermistor 89. As indicated above, the indicator light 75 is energized for a predetermined time determined solely by the resistance selected by the switch 114. For the interval timer 106 b, the resistance selected by switch 114 determines the maximum time that the heating element 84 will be energized. If a threshold temperature is exceeded during the heating cycle, this excess temperature sensed by the thermistor 89 will cause the timer 106 b to time out and interrupt power to the heating element 84.

With the present invention, the heater is only energized when a package is to be sealed. Since the heater is only energized for a predetermined length of time as determined by the rotary or slide switch 114 and thermistor 89, leaving the package on the platform will not cause continuous energization of the heater which could cause overheating. It should be noted here that the rotary or slide switch 114 which is used to connect selected external resistors to the interval timers 106 a, 106 b, can be replaced by one or more potentiometers.

It should also be noted that the present invention contemplates a sealing machine that does not have an adjustable sealing time. For this type of machine, fixed resistors may be connected to the suitable terminals of the interval timers 106 a, 106 b or, alternately, timers having a fixed time interval may be used and, thus, eliminate the need for external resistors. It should also be noted that, in the preferred embodiment, the switch 114 may comprise a three position slide switch available from Switchcraft Inc., of Chicago, Ill., under part number 502-46313LDRX. The thermistor 89 in the preferred embodiment has a resistance of 500 K ohms at 25° C.

FIG. 7A illustrates a block diagram of an alternate control system for energizing the hot plate 64. The block 100′ represents a source of power, in this case, AC power. AC power is fed to the micro-switch or cycle start switch 70 and to an off delay timer 106′ which is arranged to energize the hot plate heating element 84 for a predetermined interval upon actuation. The communication of power to the hot plate heater is actually controlled by a solid-state switch 114′. In order for the solid state switch to close and provide power to the hot plate heating element 84, it must receive an ON signal from both the off delay timer 106′ and from a thermostat 118 (which is also connected to the incoming AC power). In the preferred embodiment the thermostat 118 is attached and forms an integral part of the heating element 84. The thermostat 118 senses an overheat condition and opens to interrupt the signal or power to the solid state switch 114′ coming from the power block 100′. As indicated above, if either the signal from the thermostat 118 or from the off delay timer 106′ is terminated, the solid-state switch 114′ opens to interrupt power to the hot plate heating element 84.

FIG. 7B is a schematic for the alternate control circuit for the hot plate heater. In the illustrated embodiment, the circuit is powered from a 115 volt AC receptacle. The circuit includes a power switch 200′ which, when closed, provides power to the heated rod cutter element 58 (shown in FIG. 1A), the solid switch relay 114′ and one leg of the off delay timer 106′. The switched leg of the AC power is connected to the off delay timer 106′, the hot rod cutter 58, one side of a heat indicating light 206, one side of the thermostat 118 and one side of the heating element 84. The micro-switch 70 forming part of the hot plate platform and seen best in FIG. 3 is represented in the schematic by the double pole switch 70. It is shown with the normally open (N/O) contacts closed because when the platform is in the upper position, the plunger 72 is depressed which opens the normally closed (N/C) contacts and closes the normally open contacts. When the platform is moved downwardly by placement of the package on the heating surface 64 a, the state of the switch 70 changes so that the normally open contacts open and the normally closed contacts close. The closure of the normally closed contacts causes power to be fed to pin 9 of the off delay timer 106′ and interrupts power to pin 7. This change in switch position causes the off delay timer 106′ to send a signal to pin 3 of the solid state relay 114′ for a predetermined length of time as determined by the adjustable potentiometer 210′ that is connected across pins 5 and 6 of the off delay timer 106′. If the thermostat 118 that forms part of the heating element 84 is closed, the application of the power signal to pin 4 of the solid state relay 114′ causes power to be applied to the hot plate heater from pin 1 of the solid state relay 114. When the off delay timer 106′ times out, the interruption of signal to pin 3 of the solid state relay 114′ causes the de-energization of the hot plate heater 64.

It has been found, that with the disclosed construction and the use of the thin film graphite-based heater, continuous heating of the hot plate is not required. It has been found that the application of power to the heating element results in the heater reaching a desired temperature within 2 to 10 seconds, preferably less than 4 seconds. In short, during machine operation power is applied to the heater for only short intervals of time and, as a result, significant power savings can be realized as compared to a package-wrapping machine in which the hot plate is continuously energized.

FIGS. 8 and 9 illustrate another preferred embodiment of the invention. To facilitate the explanation, components and structures of the alternate embodiment that are the same or similar to the components and structures shown in FIGS. 1A, 1B and 2 will be given like reference characters, followed by an apostrophe.

The packaging machine shown in FIG. 8 includes a frame indicated generally by the reference character 10′. Referring also to FIG. 9, the frame 10′ comprises a lower base member 220 to which an upper base plate 224 is rigidly attached. As seen best in FIG. 8, the upper base plate 224 spans the entire width of the lower base member 220 and includes downturn flanges 224 a, 224 b which are secured to associated upturned flanges 220 a, 220 b (see FIG. 9) integrally formed in the lower base member 220. As seen best in FIG. 9, the upper base plate 224 is a continuous plate that includes a horizontal support surface 230 and a vertical wall 232 joined together by a continuous, arcuate transition 236. From the vertical wall 236, another horizontally extending plate portion 238 is formed and joins an L-shaped vertical plate 240 (see FIG. 9) which joins and rigidly attaches a rear downwardly depending flange 238 a of the upper base plate to the lower base member 220. With the disclosed construction, an extremely rigid and cost effective frame is defined by two formed, sheet metal components. The upper horizontal plate section 238, as seen in FIG. 9 in cooperation with the L-shaped vertical plate 240 defines an electrical box 46′ which houses circuitry and other components necessary for the operation of the machine (not shown). With the disclosed arrangement, the construction of the packaging machine is greatly simplified and many individual frame components used in the FIG. 1 embodiment are eliminated.

Like the embodiment shown in FIG. 1, the FIG. 8 embodiment includes a pivotally mounted plate or bridge 40′ that defines a wrapping surface 40 a′, upon which a package is wrapped with film from a supply 20′. Side plates 14′ integrally formed in the lower base member 220 include integrally formed flanges 242 that mount a heated rod cutter element 58′ and a retainer rod 50′. The bridge plate 40′is pivotable about an axle or pivot 42′ to expose the inside of the machine and to facilitate feeding of the film from the supply roll 20′. The feed path for the film is indicated by the reference character P′. As seen best in FIG. 9, the forward end of the bridge plate 40′ defines a curved rigidizing edge 40 c′. As seen best in FIG. 8, the bridge 40′ includes a pair of downwardly depending end flanges 40 b′ which overlie the outer, upper edge surfaces of the side plates 14′. This construction provides support for the bridge 40′ when rotated into its horizontal position. The illustrated arrangement is substantially similar to the arrangement shown in connection with the bridge 40 shown in FIG. 1A. It should also be noted that the curved forward edge 40 c′ of the alternate bridge plate 40′ provides a construction by which the bridge plate 40′ can be pivotally mounted so that it opens about a pivot defined by the curved edge 40 c′ and an associated pivot rod (not shown). The engagement of the upper edges of the side plates 14′ with the end flanges 40 b′ maintains a bridge plate 40′ in the horizontal position shown in FIG. 9.

The horizontal plate portion 230 of the upper base plate 224 includes a heated hot plate 64′ which may be similar or substantially the same as the hot plate 64 shown in FIG. 1A. However, the hot plate 64′ is rigidly attached to the fixed, upper base plate 224 and is not pivotally movable. In the embodiment shown in FIG. 9, a photo eye 250 is used to detect the presence or absence of a package and forms part of the heating circuit for the hot plate 64′. When a package is detected by the photo eye, 250,the heating cycle is initiated in order to heat the hot plate 64′ and thereby fuse the package film.

It should be noted that the sealing functioning performed by the packaging machine embodiment shown in FIGS. 9 and 10 is similar to sealing function performed by the packaging machine embodiment shown in FIG. 1A. However, the pivot assembly and associated plunger switch forming part of the packaging machine shown in FIG. 1A are eliminated in the packaging machine shown in FIG. 8.

The film supply 20′ is supported for rotation by a pair of supports indicated generally by the reference characters 21′, 22′, which may be the same or similar to the supports 21, 22 shown in FIGS. 1A, 1B.

The packaging machine embodiment shown in FIGS. 9 and 10 requires less individual components than the packaging machine shown in FIG. 1A. Moreover, the frame comprises only two major components, i.e., lower base member 220 and upper base plate 224. Each base member is formed from a single sheet metal and once assembled, form a rigid frame which as seen best in FIG. 9, can be easily cleaned and maintained. The elimination of the pivoting platform and the use of a continuous plate member that forms both the support surface for the hot plate and the cover for the electrical enclosure substantially reduces costs while providing surfaces that can be easily cleaned and maintained. The alternate embodiment substantially reduces the number of moving parts such as the platform assembly shown in FIG. 1A, thus reducing or eliminating a maintenance issue. In the preferred and illustrated embodiment, the lower base member and the upper base plate are formed from a continuous sheet of material, such as steel or aluminum sheet metal.

FIG. 10A illustrates a block diagram of an alternate control system for energizing the hot plate 64′ shown in FIGS. 8 and 9. The block 100′ represents a source of power, in this case AC power. Those skilled in the art will recognize that entire circuits may be DC powered. AC power is fed to the cycle start switch 250 which in this alternate embodiment preferably comprises a photo eye assembly. A photo eye assembly suitable for this application is available from Banner Engineering of Minneapolis, Minn. under the Part No. QSI18VP6D.

When the cycle start switch 250 closes, power is communicated concurrently to an interval timer 106″ and a thermostat 118′. The interval timer 106″ doses for a predetermined interval of time after energization, i.e., 5 seconds. As indicated above, power is also communicated to the thermostat 118′ which, if closed, communicates power to a temperature controller 260. In the preferred embodiment, the thermostat 118′ is located within the hot plate assembly 64′ and opens to interrupt power if the hot plate temperature exceeds a predetermined value.

If the thermostat 118′ is closed, power is communicated to the temperature controller 260, which in the preferred and illustrated embodiment is a proportional-integral-derivative (PID) controller. The controller 260 directs power to the hot plate 64′ via the interval timer 106′. The temperature of the hot plate 64′ is monitored by a feedback component such as a thermistor or thermocouple 266. At the start of the heat cycle, the temperature controller 260 communicates a substantial current to the hot plate 64′ in order to quickly heat the hot plate 64′ to a desired sealing temperature. When the preselected temperature is reached and communicated to the temperature controller 260 via the feedback component 266, the temperature controller 260 modulates the power being fed to the hot plate in order to maintain the selected temperature.

In the preferred embodiment shown in FIG. 10A, when the photo eye 250 detects a package being placed on the hot plate 64′, the temperature controller feeds sufficient power to the hot plate in order to heat it to a desired temperature within a few seconds, i.e., three. Once this temperature is reached, the temperature controller modulates power to the hot plate 64′ to maintain it at the desired temperature until removal of the sealed package is detected by the photo eye 250. If a package is inadvertently left on the hot plate platform 64′ beyond a predetermined time, i.e., five seconds, the interval timer 106″ opens to interrupt power to the hot plate 64′. In the preferred embodiment, a heat cycle cannot be reinitiated until removal of the package from the hot plate 64′ is detected by the photo eye assembly 250.

FIG. 10B is a schematic of the alternate control system/circuit for the hot plate heater that is shown in block form in FIG. 10A. The circuit is powered from 115 volt AC receptacle 264. The circuit includes a power switch 200″ which, when closed, provides power to the heated rod cutter element 58′ and a DC power supply 270. The closure of the AC power switch 200′ also communicates power to one leg or side of a solid state switch or relay 268 and one power leg of the temperature controller 260. The photo eye assembly 250 is arranged such that when placement of a package on the hot plate 64′ is detected, the photo eye assembly 250 causes power to be communicated to the other power leg or side of the solid state switch 268 causing its closure and the communication of DC power to the other leg of the temperature controller 260 and to a contact on the solid state switch 268. Power is thus communicated to the hot plate 64′ provided that the appropriate contacts of the interval timer 106″ are closed and the thermostat 118′ is closed.

In the illustrated embodiment, the hot rod cutter 58′ is powered by the same circuit as that shown in FIG. 6 and as used in the embodiment of the packaging machine shown in FIG. 1A.

As the hot plate approaches the set point temperature, the PID controller 260 begins to modulate power in an effort to reduce the rate of heating. As the set point is attained, the PID temperature controller 260 will modulate power to maintain this temperature until the system is deactivated. A potentiometer 276 forms part of the circuit and is used to modify the resistive feedback to the temperature controller 260 and provides a means by which different temperature set points can be set for the hot plate 64′.

With the disclosed circuit and package detecting methodology, a robust control circuit is provided for providing an “instant on” function for the packaging machine. It is believed that the arrangement which uses a photo eye assembly 250 for package detection causes quicker energization of the hot plate when a package is to be sealed. With the FIG. 1A embodiment, the package must be placed on the platform and the platform must pivot downwardly in order to actuate the plunger switch 70. In this alternate embodiment, as the package is moved from the wrapping platform 40′ to the hot plate 64′, its movement is detected and the heating cycle is immediately initiated even before the package to be sealed reaches the hot plate 64′. This causes the hot plate to reach its sealing temperature quicker as compared to the FIG. 1A embodiment.

It is believed that the alternate control system/circuit, reduces costs while improving functionality. It is believed that the circuit can be further simplified by eliminating what some would consider to be redundant components. For example, the temperature controller 260 can be used without the interval timer 106″. The feedback component 266 can be relied upon to control the temperature controller in order to cause it to terminate power to the hot plate when a temperature above a predetermined threshold is detected by the feedback component 266. It is believed that the thermostat 118′ may also be eliminated if the temperature controller is also used to detect an over temperature condition in the hot plate 64′ as measured by the feedback component 266.

In the disclosed embodiment, the photo eye assembly 250 works in conjunction with a DC power supply and controls the operation of the DC powered control components. The disclosed photo eye assembly operates on a supply voltage of from 10 to 30 volts DC. There are photo eye assemblies that operate with a supply voltage of 110 volts AC. If this type of photo eye assembly is employed, the DC power supply 270 could be eliminated. In fact, a photo assembly of the type that operates on a supply voltage of 110 AC can be directly substituted for the plunger switch 70 of the first embodiment (see FIGS. 3 and 6).

A suitable temperature controller is available from Crydom Inc. under Part No. MCTC2425JLA-E. A suitable solid state switch/relay is available from Crydom Inc. of San Diego, Calif. under Part No. EL240A20-US. A suitable interval timer is available from Precision Timer, a division of Prime Technology of North Branford, Conn. under part No. 843E-150. A suitable DC power supply is available from CUI Inc. of Tualatin, Oreg. under Part No. VSK-S5-24UA-T.

The invention has been described as forming part of a hand-wrapping machine use in supermarkets. However, the invention has much wider applicability. For example, it can be used in other environments such as laundry wrapping environments. It also may be used as part of automated wrapping machines used in various industries. Accordingly, the present invention should not be limited to wrapping machines of the type found in supermarkets.

Although the invention has been described with a certain degree of particularity, those skilled in the art can make various changes to it without departing from the spirit or scope of the invention as hereinafter claimed. 

1. A packaging machine for wrapping a package with a stretchable film, the packaging machine having a frame defining a wrapping surface, a supply of wrapping film accessible by an operator, a means for severing a length of film used to wrap a package from the supply and a hot plate including a heating element for fusing at least a portion of the film that is wrapped around the package, said packaging machine comprising a package sensor for sensing the presence of a package to be sealed, said sensor forming part of a heating circuit for said heating element that applies power to said heating element when a package is sensed, said sensor comprising a photo eye assembly arranged such that it senses a package to be sealed as it is placed on said hot plate.
 2. The apparatus of claim 1 wherein said heating element is energized for as long as a package to be sealed is sensed by said photo eye assembly.
 3. The apparatus of claim 1 further including a temperature response device associated with said heating element for deenergizing said heating element if a predetermined operating temperature is exceeded.
 4. The apparatus of claim 1 further comprising a temperature controller which modulates power to said heating element to maintain said heating element at a predetermined temperature.
 5. The apparatus of claim 4 further comprising a feedback component which senses temperature of said heating element and communicates with said temperature controller.
 6. The apparatus of claim 5 wherein said feedback component comprises a thermistor.
 7. The apparatus of claim 3 wherein said temperature responsive device is a thermostat.
 8. The apparatus of claim 1 further comprising an interval timer for controlling a maximum time that said heating element can be energized.
 9. The apparatus of claim 1 wherein said frame comprises: a) a lower base member having integrally formed side plates and laterally extending tabs defining a mounting location for a cut-off rod and at least one upturned mounting flange; b) an upper base plate defining a substantially horizontal support surface for said hot plate and a vertical wall interconnected with said support surface by a curved transition portion and further including a substantially laterally extending enclosure portion for defining a portion of a hardware enclosure located between the side plates of said lower base member when said upper base plate is mounted to said lower base member; and c) said upper base plate further including at least one downwardly depending flange that is engageable with said upturned flange of said lower base member.
 10. A packaging machine for wrapping a package with a stretchable film, the packaging machine having a frame defining a wrapping surface, a supply of wrapping film accessible by an operator, a means for severing a length of film used to wrap a package from the supply and a hot plate including a heating element for fusing at least a portion of the film that is wrapped around the package, said packaging machine comprising: a) a lower base member having integrally formed side plates and laterally extending tabs defining a mounting location for a cut-off rod and at least one upturned mounting flange; b) an upper base plate defining a substantially horizontal support surface for said hot plate and a vertical wall interconnected with said support surface by a curved transition portion and further including a substantially laterally extending enclosure portion for defining a portion of a hardware enclosure located between the side plates of said lower base member when said upper base plate is mounted to said lower base member; and c) said upper base plate further including at least one downwardly depending flange that is engageable with said upturned flange of said lower base member.
 11. The apparatus of claim 10 further comprising a vertical plate member for joining said enclosure portion of said upper base plate with said lower base member.
 12. The apparatus of claim 10 wherein said vertical wall portion mounts said photo eye assembly.
 13. The apparatus of claim 10 further comprising a bridge plate pivotally mounted between said side plates of said lower base member.
 14. The apparatus of claim 5 wherein said feedback component comprises a thermocouple.
 15. The apparatus of claim 10 wherein said lower base member and said upper base plate are formed from a substantially continuous metal sheet.
 16. A packaging machine for wrapping a package with a stretchable film, comprising: a) a supply of wrapping film accessible by an operator and a frame defining a wrapping surface; b) a heated rod for severing said film; c) said frame defined by a lower base member and an upper base plate, said base member and upper plate formed from a continuous sheet material; d) a hot plate for fusing at least a portion of the film that is wrapped around a package; e) an optical sensor for sensing the presence of a package to be sealed on said hot plate, said sensor forming part of a heating circuit for communicating power to said hot plate when a package is sensed.
 17. The packaging machine of claim 16 wherein said optical sensor is a photo eye assembly.
 18. The packaging machine of claim 17 wherein said upper base plate defines a support surface for said hot plate, a substantially vertical portion to which said photo eye assembly is mounted and a lateral portion at least partially defining an enclosure. 